Season Cracking •
Different Types of
- Recognition, Mechanisms & Prevention
Stress Corrosion Cracking (SCC)
What is stress corrosion cracking?
Stress-corrosion cracking (SCC) is a cracking process that requires
the simultaneous action of a corrodent and sustained
tensile stress. This
excludes corrosion-reduced sections
that fail by fast fracture. It also
excludes intercrystalline or transcrystalline corrosion, which can
an alloy without
applied or residual stress. Stress-corrosion
cracking may occur in combination with hydrogen embrittlement.
The image of stress corrosion I see
Is that of a huge unwanted tree
Against whose trunk we chop and chop,
But which outgrows the chips that drop;
And from each gash made in its bark
branch grows to make more dark
The shade of ignorance around its base,
Where scientists toil with puzzled face.
(by S P Rideout 1967)
What causes stress corrosion
Stress corrosion cracking results from the conjoint action of
three components: (1) a susceptible material; (2) a specific chemical
species (environment) and (3) tensile stress. For example, copper and its
alloys are susceptible to ammonia compounds, mild steels are susceptible to
alkalis and stainless steels are susceptible to chlorides.
There is no unified mechanism for stress corrosion
cracking in the literature. Various models have been proposed which include
Adsorption model: specific chemical species adsorbs on
the crack surface and lowers the fracture stress.
Film rupture model: stress ruptures the passive film
locally and sets up an active-passive cell. Newly formed passive film is
ruptured again under stress and the cycle continues until failure.
Pre-existing active path model: Pre-existing path such as
grain boundaries where intermetallics and compounds are formed.
Embrittlement model: Hydrogen embrittlement is a major
mechanism of SCC for steels and other alloys such as titanium. Hydrogen
atoms diffuse to the crack tip and embrittle the metal.
How to prevent
stress corrosion cracking? Stress corrosion cracking can be prevented through:
- Avoid the chemical species that causes SCC.
- Control of hardness and stress level (residual or load).
- Introduce compressive
stress by shot-peening for example.
- Use of materials known not to crack in the specified environment.
- Control operating temperature and/or the electrochemical potential of
For more details
|More details on stress corrosion
cracking are included in the following
corrosion short courses which you can take as
in-house training courses,
courses or distance
Corrosion and Its Prevention (5-day module)
API 571 Damage Mechanisms Affecting Fixed Equipment in the Refining and
Petrochemical Industries (5 days)
Environmental Cracking (HB/HIC/SWC/SOHIC/SSC/SZC/HSC/HE/SCC):
Recognition, Mechanisms and Prevention (5 days)
Inspection, Testing and Monitoring: Techniques and Applications (5)
Corrosion, Metallurgy, Failure Analysis and
Marine Corrosion, Causes and Prevention
Materials Selection and Corrosion
Stainless Steels and Alloys:
Why They Resist Corrosion and How They Fail
Corrosion Control and Prevention in Seawater Desalination Plants (1
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